1. Field of the Invention
The present invention relates to a fuel pump assembly sucking a fuel in a fuel tank and pressurizing the sucked fuel for supplying to a fuel supply system associated with an internal combustion engine. More particularly, the invention relates to a fuel pump assembly performing pumping operation by reciprocally driving a push rod or a diaphragm by means of an eccentric cam fixedly mounted on a camshaft of an internal combustion engine and increasing and decreasing a volume of a pumping chamber through a pump diaphragm by reciprocal motion of the push rod or the diaphragm.
2. Description of the Related Art
The conventional fuel pump assembly is illustrated in FIG. 2. In FIG. 2, the reference numeral 1 denotes a lower pump body, an upper end 1A of which forms a flat surface. A recessed portion 1B defining an operation chamber and opening to the upper end 1A is defined in the lower pump body 1. Also, a downwardly opened push rod guide bore 1E with an upper bottom portion 1D located at higher position than a lower end 1C, is formed in the lower pump body 1. The reference numeral 2 denotes an upper pump body arranged on the upper end 1A of the lower pump body 1. A recessed portion 2B for defining a pump chamber is defined in the upper pump body 2 and is located in opposition to the recessed portion 1B when the upper pump body 2 is assembled with the lower pump body. Also, a recessed portion 2D for defining an inflow chamber and a recessed portion 2E for defining a discharge chamber, both opening to an upper end 2C of the upper pump body 2, are formed. The recessed portion 2D for defining the inflow chamber and the recessed portion 2E for defining the discharge chamber are separated by a partitioning wall 2F. The recessed portion 2D for defining the inflow chamber and the recessed portion 2E for defining the discharge chamber are communicated through an inflow hole 2G. The recessed portion 2B for defining the pump chamber and the recessed portion 2E for defining the discharge chamber are communicated through a discharge hole 2H. The reference numeral 3 denotes a suction side check valve for opening and closing the inflow hole 2G. The reference numeral 4 denotes a discharge side check valve for opening and closing the discharge hole 2H. The reference numeral 5 denotes a pump cover arranged on an upper end 2C of the upper pump body 2. The lower end 5A of the pump cover 5 defines a recessed portion 5B defining a first regulator chamber opposing the recessed portion 2D for defining the inflow chamber and a recessed portion 5C defining a second regulator chamber opposing the recessed portion 2E for defining the discharge chamber, are formed in the pump cover 5. The reference numeral 5D denotes a partitioning wall separating the recessed portion 5B defining the first regulator chamber and the recessed portion 5C defining the second regulator chamber.
Then, on the upper end 1A of the lower pump body 1, the upper pump body 2 is arranged, Also, on the upper end 2C of the upper pump body 2, the pump cover is arranged. The lower pump body 1, the upper pump body 2 and the pump cover 5 are fixedly assembled by means of bolts 6. At this time, between the upper end 1A of the lower pump body 1 and the lower end 2A of the upper pump body 2, a pump diaphragm 7 is clamped. Similarly, between the upper end 2C of the upper pump body 2 and the lower end 5A of the pump cover 5, a regulator diaphragm 8 is arranged. By the pump diaphragm 7 and the recessed portion 1B defining the operation chamber of the lower pump body 1, an operation chamber A is defined. Also, by the pump diaphragm 7 and the recessed portion 2B for defining the pump chamber of the upper pump body 2, a pump chamber P is defined. On the other hand, by the regulator diaphragm 8 and the recessed portion 2D for defining the inflow chamber of the upper pump body 2, an inflow chamber B is defined, and by the regulator diaphragm 8 and the recessed portion 2E for defining the discharge chamber, the discharge chamber C is defined. The inflow chamber B and the discharge chamber C are separated by the partitioning wall 2F. Also, by the regulator diaphragm 8 and the recessed portion 5B for defining the first regulator chamber of the pump cover 5, a first regulator chamber D is defined and by the regulator diaphragm 8 and the recessed portion 5B for defining the second regulator chamber of the pump cover 5, a second regulator chamber E is defined. The first regulator chamber D and the second regulator chamber E are separated by the partitioning wall 5D. Also, the first regulator chamber D is in opposition to the inflow chamber B via the regulator diaphragm 8, and the second regulator chamber E is in opposition to the discharge chamber C via the regulator diaphragm 8.
On the pump diaphragm 7, a diaphragm rod 9 is integrally mounted via upper and lower retainers. The diaphragm rod 9 is arranged within the rod guide hole 1G extending from the operation chamber A to the push rod guide hole 1E in movable fashion. The lower end is located in the vicinity of the lower end of the push rod guide hole 1E.
The reference numeral 10 denotes a cylindrical push rod slidably supported in the, push rod guide hole 1E at an outer diametrical portion 10A and is slidably supported on the diaphragm rod 9 at the inner diametrical portion 10B. On the push rod 10, an upwardly opened recessed portion 10D opened upwardly and having a bottom portion 10C and an elongated groove 10E cut out from the inner diametrical portion 10B to the outer diametrical portion 10A. Within the elongated groove 10E, a pin 11 is mounted in the vicinity of the lower end of the diaphragm rod 9.
The reference numeral 12 denotes a push rod spring disposed within the push rod guide hole 1E in compressed position. The upper end of the push rod spring 12 is engaged with an upper bottom portion 1D of the push rod guide hole 1E. The lower end is engaged with the bottom portion 10C of the upwardly opened recessed portion 10D of the push rod 10. The push rod spring 12 downwardly depresses the push rod 10 to engage the push rod 10 with the pin 11. On the other hand, within the operation chamber A, a diaphragm spring 13 is disposed within compressed position. The upper end of the diaphragm spring 13 is engaged via the retainer, and the lower end of the diaphragm spring 13 is engaged with the recessed portion 1B of the operation chamber. The diaphragm spring 13 depresses the pump diaphragm 9 toward the pump chamber P.
Then, a relationship of spring forces between the push rod spring 12 and the diaphragm spring 13 is set, in the condition illustrated in FIG. 2, such that a spring force of the push rod spring 12 is set greater than a spring force of the diaphragm spring 13. Then, when the fuel pump arrangement is installed on a not shown internal combustion engine, the lower end of the push rod 10 projecting downwardly from the lower end 1C of the lower pump body 1 is arranged in contact with the eccentric cam mounted on the camshaft (camshaft and eccentric cam are not shown).
In the construction set forth above, when the engine is driven and a high profile portion of the eccentric cam comes into contact with the push rod 10, the push rod 10 is moved upwardly against a spring force of the push rod spring 12 to reduce a volume of the pump chamber P of the pump diaphragm 7. By this, the suction side check valve 3 closes the inflow hole 2G and the discharge side check valve 4 opens the discharge hole 2H. By this, the fuel stored in the pump chamber P is pressurized and discharged to the discharge chamber C and then supplied to the fuel supply system via a not shown duel discharge passage. Next, when the low profile portion of the eccentric cam comes into contact with the push rod 10, the push rod 10 is depressed downwardly toward the low profile portion of the eccentric cam by the spring force of the push rod spring 12. Movement of the push rod 10 is transmitted to the diaphragm rod 9 via the pin 11 to increase the volume of the pump chamber P by shifting the pump diaphragm 7 downwardly. Then, tie suction side check valve 3 opens the inflow hole 2G and the discharge side check valve 4 closes the discharge hole 2H. By this, the fuel in a not shown fuel reservoir, such as a fuel tank, is sucked into the pump chamber P via the inflow hole 2G. Then, by sequential rotation of the eccentric cam, suction of the fuel into the pump chamber P and discharging therefrom is sequentially performed. Thus, the fuel stored in the fuel reservoir can be continuously supplied to the fuel supply system from the fuel pump assembly.
In such fuel pump assembly, movement of the diaphragm rod 9 including the push rod 10 and the pump diaphragm 7 toward the side for increasing the volume of the pump chamber P (in other words, movement downwardly in the drawing) depends on the spring force of the push rod spring 12, as set froth above. In order to enhance follow-up ability of the push rod 10 when rotation speed of the eccentric cam is significantly increased, it is typical to increase the spring force of the push rod spring 12. In order to increase the spring force of the push rod spring 12, it is typical to increase external diameter of the push rod spring 12. If the external diameter of the push rod spring 12 is increased, it becomes necessary to increase diameter of the push rod guide hole 1E to inherently cause increasing of size of the cylindrical portion of the lower pump body 1. Thus, freedom in installing on the engine can be degraded.